Ok, I am pretty green when it comes to woodworking, but that aside, I am trying what I thought was going to be a simple project (but clearly this is beyone my knowledge base). Here is what I have:
I would like to build some trapezoid planter boxes for my deck. I am looking to make them 12″x16′” for the base and taper to 16″x20″ on the top. I want to use 2×2 for the base and top and will also be using 2×2 for the four side braces. I am hoping to tongue and groove the bases and edges. I will use 1×4 to create the sides, again using tongue and groove to slide them in.
Here’s my biggest issue: what compound mitre do I need to use (for all the cuts)? I have been working with google sketchup and basic graph paper to figure this all out to no avail. I can’t find any formulas for a trapezoid that is not equidistant, so I tried to get some pyramid ideas because my trapezoid is essentially the bottom part of the pyramid.
Here are a few places I have been looking but still can’t figure it out:
http://forums.finewoodworking.com/fine-woodworking-knots/joinery/trapezoid-miteres
http://www.flickr.com/photos/rndmodelshop/4598051596/sizes/m/in/photostream/ – This is kinda what I’m thinking frame wise (but obviously a trapezoid vice pyramid)
http://jansson.us/jcompound.html#pyramid – Pyramid calculator that I don’t know how to read but think is what I need
http://www.pdxtex.com/canoe/compound.htm – 85% of what I am looking for, but the but joints won’t work as I will have 2×2 running up the edges…
Any and all help will be more than appreciated! I have the necessary tools, but obviously lack the know-how. Thanks in advance everyone.
Replies
Angles
I hate figuring this stuff out - but I'm sure there are folks here who will advise you correctly. I've read Tage Frid's books - and they will help if you read them - but for myself when I have these cutting issues - I find it easier to cut the angles into the wood boards first - then do the bevel on the edges -
Hope this helps -
SA
A little work
If you play a little more with sketch up you will find that if you cut 4 trapezoid pieces they will meet at the corners at 90 degrees. It may not be so evident in my drawing, but trust me it is. I would suggest you use some sort of butt joint on the planter. I like to use one with a dado and a quirk left at the corners as they are attractive and not hard to make. The angle on the top or the parallel sides you need to rip to make the sloped pieces meet the top and bottom should be easy to work out with drafting.
If you are clever with trig you could work it out, I think as the tangent or arc tangent of 1.5 divided by 10...one of those ratio and table things.
Peter
make a model
I was watching an episode of Rough Cut with Tommy Mac last weekend. He made a serving tray which is essentially what you are trying to do. The secret was to take a block of wood and cut the bevels on it that represent the outside of your planter.
Then you use that to set your table saw blade angle and or miter gauge angle to get the compound miter. It was a pretty neat idea.
Picture from his web page:
http://www.thomasjmacdonald.com/content/wp-content/uploads/2010/09/Thumb109.png
Magazine tells how to make a setup block
The April/May issue of "American Woodworker" page 37 describes how to make a setup block for any angle. Also AmericanWoodworker.com/WebExtras
Drawings
Perhaps I don't understand the problem, but often the solution is a drawing. Attached is a sample that gives answers of 81 degrees to bevel the top and bottoms of the side trapezoid pieces roughly based on my understanding of your question. The sides meet each other at 90 degrees so a but joint or miter at 45 degrees if you want to complicate things.
Hope these help.
Peter
how does one adjust to make a triangular-shaped object with splayed sides?
Thx
This table might answer your questions. It's a page from a 1950 Craftsman table saw manual. I've used the table several times and it's quite accurate, or so it seemed.
RM
spreadsheet here: https://s26462.pcdn.co/wp-content/uploads/calc.xls
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